Ecology and Conservation
Isotachis (red liverwort) growing on soil at forest edge (photo by J. Braggins) |
The ecological importance of bryophytes, including their role in succession, production and phytomass, herbivory, decomposition, and nutrient cycling is reviewed by Longton (1984, 1992). A series of 16 papers published by the Botanical Journal of the Linnean Society in 1990 as part of an International Symposium on Bryophyte Ecology also provides an excellent account of the significance of bryophytes in various ecological systems. Studies in Central and South America have shown that bryophytes play a significant role in contributing to nutrient cycles (Coxson, McIntrye & Vogel, 1992), and they also form a major component of canopy humus (Ingram & Nadkarni, 1993). In that system, the canopy humus is exploited by numerous organisms, including canopy vascular plants, birds, and invertebrates (Nadkarni and Longino, 1990). Interestingly, there is evidence to suggest that changes in epiphytic bryophyte assemblages affect other canopy dwelling biota, such as vascular epiphytes, invertebrates, and especially foraging birds (Sillet, 1994). Furthermore, Pócs (1980) established that bryophytes are very effective rainfall interceptors, and that the overwhelming abundance of epiphytic liverworts in “cloud” or “mossy” forest zones is considered an important factor in eliminating the deteriorating effect of heavy rains, including helping to prevent soil erosion and adding to hill stability. Gignac (2001) concluded that because of the close association of bryophytes with climatically sensitive habitats and ecosystems, they may serve as potential indicators of large-scale changes to an ecosystem before the habitat or ecosystem itself is affected.
Epiphytic liverworts and mosses covering tree trunks in a Nothofagus forest (South Island, New Zealand; photo by C. Davis) |
Habitats
Liverworts are found literally everywhere. They flourish on every
continent and landmass, including Antarctica, and exploit a remarkably
diverse array of microhabitats. In addition to growing in persistently
moist environments, such as in fresh water, on forest floors, waterfall
splash zones, and stream banks, some are well adapted to microhabitats
where water is limited. These include on bark and twigs (epiphytes),
on the surface of leaves (epiphylls), and on rock surfaces. Some
liverworts are even able to persist in truly desert environments. The
ocean and other salty aquatic habitats are the only environments where
liverworts are absent.
Liverworts and mosses in a seepage bank (photo by M. von Konrat) |
Conservation
The IUCN (International Union for Conservation
of Nature and Natural Resources; see also the IUCN
Bryophyte Specialist Group) lists
merely 45 species of liverworts as threatened worldwide, and this is
likely a vast underestimate. Difficulties in applying IUCN guidelines
to bryophytes contribute to this underestimate. For example, data
are seldom available to bryologists that would make it possible to conduct
population viability analyses, calculate generation time, or estimate
the number of mature individuals or total population sizes. Evaluation
of species against the threat categories is mostly based on numbers of
collections and inference from available data. Furthermore, some
of the criteria are either not applicable, inappropriate, or present
special challenges when dealing with bryophytes. For example, it
is difficult to apply the term ‘individual’ as defined by
Molloy et al. (2002) [the number of mature individuals is defined as
the number of known, estimated or inferred to be capable of reproduction]. In
setting forth guidelines for the application of the revised IUCN threat
categories specifically to bryophytes, Hallingbäck et al. (1998)
noted that it is impossible, without genetic studies of each unit, to
determine what constitutes an individual bryophyte.
Anthelia juratzkana, growing like asphalt in an alpine meadow (photo by C. Davis) |
An epiphytic Frullania (photo by M. von Konrat) |
Threats of forest fragmentation
Recent work has shown that habitat fragmentation significantly affects
bryophyte biodiversity in low boreal (Gignac et al., 2005) and Amazonian
forests (Zartman, 2003, 2006). These studies suggest that fragment
size is the determining factor in preserving bryophyte biodiversity. Limitations
to dispersal may explain why smaller fragments have a greater probability
of local extinction (Zartman, 2006).
.gif){kind=logo}